Sore throats are often treated by sucking a sugar-based lozenge. The lozenge contains at least one compound which is active against sore throats. In addition, the sucking action results in the production of saliva which lubricates the throat and reduces the pain and discomfort experienced by an individual.
A boiled sugar lozenge is a ‘glass’ or supercooled liquid, and at extremely high viscosity has an amorphous non-crystalline state. In this state, other constituents can be dissolved or suspended (colours, flavours, pharmacological actives etc). The moisture content of such a lozenge is low (c. 2%). Some of this moisture is in a ‘free’ state, but much of the moisture is not. This gives a stable chemical and physical environment.
However, small increases in the moisture content of such lozenges have the following detrimental effects. The viscosity of the ‘glass’ is reduced, which leads to a gradual ‘cold flow’ of the lozenge. The presence of ‘free’ water provides a reaction medium in which accelerated degradation of added components can occur. Water causes the lozenge to become sticky and both unattractive and difficult to handle by packing equipment or by the user. Water is involved in hydrolysis of the disaccharide bond in sugar, catalysed under acid conditions provided by the typical inclusion of flavour enhancing organic acids. Cleavage of the disaccharide bond forms glucose and fructose, which are both more hygroscopic than sugar (sucrose) and tend to accelerate the absorption of further water from the surrounding environment. The reduction in the sugar content compromises the physical hardness of the lozenge. In some cases complete liquefaction of the lozenge can occur. As the absorption of water is an accelerative process, low initial water content and the exclusion of even small quantities of water from the lozenge environment are important to maximise shelf life. For a medicated lozenge containing pharmaceutical ingredients, the issue of stability is particularly significant as compared to confectionery lozenges. For example, a much longer shelf life required of medicinal products, the health risks associated with chemical change mediated by increased water content, and the higher value of the goods spoiled.
It would, therefore, be desirable to develop an alternative product for treating sore throats which avoids the use of a sugar-based lozenge.